SPY VS SPY

I was 21 years when I wrote this song
I'm 22 now, but I won't be for long...

These, of course, are the opening lines to A New England by Billy Bragg, from lo, those many years ago.

But it was just yesterday that those lyrics put me in a crisis.

Let’s parse the ontology, as the French kids like to say...

One would think that the phrase “wrote this song” is meant comprehensively, that is, I wrote the music and the words. But if that is indeed the case, how does that “now” come into play?

Did he write the song when he was 21 with a different second line? Say,

I was 21 years when I wrote this song
Donkey Kong, Donkey Kong, Donkey Kong

Then, by the time he scored a record deal and hit the studio, he was 22 and updated the lyric to its present state?

That has to be it. Otherwise, this song bends all known laws of temporal physics. And gives me a splitting headache to boot...